I think we need parallel sections. Basically a getting started guide that assumes Nova Networking and a getting started guide that assumes Quantum networking.
Hopefully the differences between these two paths can be isolated to a few sections, vs. needing two separate documents.

To ensure proper coverage here we need to provide:
1) Accurate documentation for using Nova networking.
2) Accurate documentation for using Quantum networking.
3) Contrast between the two (pros/cons) and guidance *not* to use both at the same time.
It is unclear based on the comments so far that there is a specific preference for RHOS users to use one over the other so in the meantime we need to treat both as equal citizens.

I've added this "important" admonition:
"Red Hat OpenStack compute services also support networking using the OpenStack Network Service. If you wish to use the OpenStack Network Service to provide networking services to your compute instances then do not create a network using the nova-manage command."

commit fcac794de9bcfd5e37efcd98bf891dd7c4eaf4bb
Author: Stephen Gordon <sgordon@redhat.com>
Date: Tue Feb 12 15:16:24 2013 -0500
BZ#888812 - Users wishing to use ONS should not use nova-manage to create network.
Added an admonition advising users wishing to use the OpenStack
Network Service for instance networking not to create a network
using nova-manage.

commit fdb0453989888a6e875f6ca85c592edf9d1e2aac
Author: Stephen Gordon <sgordon@redhat.com>
Date: Wed Feb 13 14:56:40 2013 -0500
BZ#888812 - Updated instructions for avoiding Nova network when planning to use ONS
For users wishing to use the OpenStack network service instead of the Nova
network service made the following changes:
- Added instruction to skip start of openstack-nova-network service in Nova chapter.
- Added instruction to skip nova-manage network create in Nova chapter.
- Added instruction to OpenStack Network chapter specifying the Nova service to restart once
the node is configured for OpenStack Network.

Moving back to assigned, I missed a word and made a spelling mistake here. The admonition currently reads:
"Do not use the service or chkconfig commands to start the openstack-nova-network if you intend to install and configure the OpenStack Network service to manage the networking for your enviornment."
Need to add the work service after openstack-nova-network and spell environment correctly.